Fig. 6. Copper²⁺ adsorption on goethite with 0.01 M NaNO₃ background electrolyte. Cu_T = 0.785 mM. Goethite concentration 10 g L^-1, specific surface area 50 m² g^-1. Open symbols represent experimentally determined Cu adsorption. Filled symbols with dotted lines represent adsorbed Cu species based on optimized CD-MUSIC fit to experimental data. Solid line represents cumulative total of adsorbed Cu species predicted by CD-MUSIC model.